Method and apparatus for producing radio beacons



Jam 22, M43. P. J. HOLMES METHOD AND APPARATUS FOR PRODUCING RADIOBEACONS I Filed April 17, 1939 2 Sheets-Sheet l Osc/LLA 702 a 4 4 2 J J3 2 k 0 m mm MW Wm WM a PA E J of 7 9 m P 5 m a 1 1 1 2 F EF lg Mm 5M 60m 4 M awe/who e .PAUL J HOLMES,

Patented June 22, 1943 REETHQD AND APPARATUS FUR PRODUCING RADIO BEACONSPaul J. Holmes, Los Angeles, Cailif., assignor to William H. Donnelly,Los Angeles, Calif.

Application April 17, 1939, Serial No. 268,172

8 Claims.

This invention relates to methods and apparatus for providing radiobeacon courses.

Systems have been previously proposed which use a single pair ofvertical radiators which radiate an identifiable signal in accordancewith one lobular horizontal directivity pattern when fed in one phaserelation and another identifiable signal in accordance with a secondpattern overlapping the first pattern when fed in another phaserelation. The two overlapping patterns thus provide equi-signal radiobeacon courses. The phase changing in the currents supplied to theradiators has heretofore been accomplished through the use of mechanicalor electromechanical switching arrangements. This introducescomplications which increase the cost of construction and maintenance.

A particular object of this invention is to provide simple methods andapparatus for produc ing a plurality of directive radio beacon courseswith two spaced radiators by changing the phase of the currents at theradiators by purely electrical means and without using any mechanical orelectromechanical switching arrangements for phase changing.

Another object of the invention is to provide methods and apparatus forproducing a multicourse directive radio beacon which will produce visualor aural indications or a combination thereof along with code or voicecommunication.

A further object of the invention is to provide simple methods andapparatus for producing directive radio beacon courses which usesuppressed carrier transmission and resupply the carrier frequency tothe transmitted signal in space.

According to this invention I supply a wave resulting from modulation ofa carrier wave of given frequency to the first side of a phaseshiftingnetwork which has a radiator connected thereto. I also supply a waveresulting from modulation of a carrier Wave of the same given frequencyto the second side of said network which has a radiator connectedthereto, which radiator is spaced from said first named radiator. Eachof said supplied Waves may comprise, for example, a modulated carrierwave including both side bands, or it may comprise the two side bandsfrom which the carrier wave has been suppressed, or it may comprise asingle side band from which the carrier and the other side band has beensuppressed. Said waves supplied to the opposite sides of said networkmay result from modulation by the same modulation frequency or they mayresult from modulation by two different and preferably audiblemodulation frequencies. The phase relation between the waves radiated ateach of said radiators determines the horizontal directivity pattern ofthe combined wave radiated by said radiators and due to the phaseshifting network. between said radiators and the manner in which wavesare supplied to said radiators and to said network, the phase relationbetween the radiated waves is periodical 1y shifted causing theradiators toradiate periodically changing horizontal directivitypatterns. As brought out subsequently, these patterns may be madeidentifiable in such manner as to provide equisignal radio beaconcourses.

We may assume for the purposes of illustration that amplitude modulatedwaves are directly supplied to the opposite sides of the net'- work andare of the same amplitude, and'that one wave is modulated by one audiofrequency modulation signal and the other by a different audio frequencymodulation signal and that the carriers of said waves are in phase upontheir arrival at the network. As the two waves go through their cyclicchanges in amplitude at the opposite sides of the network, there will beinstants of time in which the two waves are of equal amplitude and otherinstants in which one wave has a finite amplitude while the other iszero and still other instants in which said other wave has a finiteamplitude and said one wave is zero. Assuming for the sake of simplicitythat a wave traveling from either side of the net work to the radiatorconnected to that side undergoes the same phase shift (although this isnot necessary as will be brought out subsequent- 1y), it may be seenthat the radiators radiate in phase when the waves are of equalamplitude and out of phase by the amount of phase shift provided by thephase-shifting network, say when either one of the waves is at zero andthe other wave has a finite amplitude. The directivity pattern producedwhen one wave has zero amplitude and the other wave has a finiteamplitude is similar to the pattern radiated when the reverse relationbetween the two waves is obtained; however, the two patterns arereversed in space since the phase shift applied to each wave isadditive. By proper spacing of the radiators, preferably more thanone-fourth the carrier frequency wavelength, say three-fourths thewavelength, the two patterns overlap. One of these overlapping patternsis due primarily to one of the modulated waves and the other isprimarily due to the other modulated wave. Hence in the zones where thepatterns overlap the two signals are radiated with equal intensity andprovide equi-signal radio beacon courses. In the intervals of timebetween the in phase radiation and the 90 out of phase radiation, theradiation pattern changes through successive patterns from the in phasepattern to the 90 out of phase pattern to produce one set of patternsand vice versa. One set of patterns is produced predominantly by theaction of one of the modulated waves and the other is producedpredominantly by the ac tion of the other of the modulated waves.

As brought out above, I may radiate the carrier and both side bands fromthe above-mentioned radiators or I may suppress the carrier and radiateonly one or both the side bands. In the latter cases I resupply thecarrier to the radiated waves by radiation from a non-directive thirdradiator which radiates the carrier in the proper time phaserelationship. This last system has some advantages in that theresupplied carrier may also be modulated by voice or code signals forcommunication purposes.

Further objects of my invention will become apparent when my inventionis described in conjunction with the accompanying drawings in which:

Fig. 1 is a diagrammatic illustration of a simple form of my invention;

Figs. 2,3, and 4 are horizontal directivity patterns which may beobtained with the apparatus illustrated in Fig. 1;

Fig. is a diagrammatic illustration of a modifled form of my invention;

Fig. 6 illustrates horizontal directivity patterns which may be obtainedwith the apparatus illustrated in Fig. 5; and

Fig. 7 is a diagrammatic illustration of a receiving apparatus which maybe used to identify the beacon courses provided by the apparatus shownin Figs. 1 and 5.

Referring to Fig. 1, a suitable carrier power source such as a masteroscillator ID oscillating at any desired frequency, say 3 megacycles, isshown connected to modulators II and I2 which are respectively connectedto power amplifiers I3 and I4. amplitude modulate the radio frequencycarrier with different and distinct audio frequency modulation signals,say 65 and 86.7 cycles, so that the amplitude modulated waves deliveredthereby may be separately identifiable after radiation. For reasonswhich will appear later the modulators preferably operate to produce100% modulation of the carrier. The power amplifiers I3 and I4 are shownconnected respectively to transmission lines I5 and I6 leading todifferent sides of a phase-shifting network I! operable to produce aphase-shift of 90, for example, in the current traversing thephase-Shifting network. The remaining ends of the transmission lines I5and I6 are shown connected through suitable' coupling network I8 and I 9to radiators and 2| respectively. The radiator 20 and 2| may comprisevertical radiators having a length comparable to one-quarter of thewavelength of the carrier frequency supplied by the master oscillatorIll and the two radiators 20 and 2| may be spaced horizontally from oneanother by any convenient distance, preferably greater than a distanceequal to one-quarter the carrier wavelength, for example, by a distanceof about threequarters of a carrier wavelength.

The amplitude modulated waves delivered by the power amplifiers I3 andI4 are separately The modulators II and I2 preferably identifiable, andfor the purposes of illustration it may be assumed that the carrierfrequency contained in each of these modulated waves is delivered inphase to the opposite sides of the phase-shifter IT. This may beaccomplished by introducing suitable phase-shifting networks in eitherone or both of the branch circuits leading from the power amplifiers I3and I4 as shown at I3a and Ma, if required. Also, in the interests ofclarity, we may assume that the amplitudes of the modulated wavesdelivered by the power amplifiers l3 and M are equal.

At a given instant of time and at the opposite sides of the network II,the -cycle modulated wave may have a maximum amplitude, while the86.7-cycle wave may have zero amplitude. At this instant, assuming thatcurrents supplied by the amplifiers I3 and I4 are in phase at theopposite sides of the phase-shifter ll, radiation from both antennae 2i)and 2| will be due to power amplifier l3 which is modulated by the65-cyc1e tone. Due to the action of the phase-shifting network II,currents radiated from the radiator 2| will be out of phase withcurrents radiated from the radiator 28, assuming that characteristics ofthe transmission lines I5 and I6 and coupling devices I8 and I9 are thesame. This will cause the radiators to radiate predominantly a 65-cyclewave in accordance with a lobular horizontal directivity pattern, asshown in full lines at 3|] in Fig. 2. V

In Figs. 2, 3, and 4 the radiators 20 and 2| are located on ahorizontally extending line R R, symmetrically disposed with respect tothe centers of thecircles surrounding the directivity patternsillustrated in said figures. The patterns are plotted in polarcoordinates to represent the relative amplitudes of the radiated signalsas transmitted in any horizontal direction from the centers of thecircles at distances which are great compared to the distances betweenthe radiators 2!) and 2 I.

At some later instant of time, the amplitude of the 65-cycle modulatedwave delivered by power amplifier I3 will be somewhat less than maximum,but will still be somewhat greater than the amplitude of the 86.7-cyclemodulated wave delivered by the power amplifier I4 to the opposite sideof the phase-shifting net-work H,

which last-named Wave is now greater than zero and is approaching itsmaximum. As a consequence, the resultant currents radiated by theantennae 20 and M will be somewhat less than 90 out of phase, forexample about 45 out of phase, and will be radiated in accordance with alobular horizontal directivitypattern as shown in full lines at 3| inFig. 3. This pattern, like the pattern 30. will still be separatelyidentifiable since it results primarily from the radiation of a 65-cyclemodulated wave.

As the (id-cycle modulated wave continues to diminish in magnitude andthe SSH-cycle modulated wave continues to increase in magnitude, thelobular pattern as shown in full lines at 30 and 3| in Figs. 2 and 3becomes more nearly symmeirical with respect to a line perpendicular tothe line RR and becomes symmetrical with respect to said perpendicularline when the two waves are of equal amplitude and the resultantcurrents at the radiators are in phase, as shown in full lines at 32 inFig. 4. The pattern illustrated at 32 exists only for an instant andthen the 86.7-cycle modulated Wave delivered by the amplifier I4 has agreater amplitude than the 65-cycle modulated Wave delivered by theamplifier I3. Since the amplitude relation is now opposite to thatdescribed above, the phase-shift is effectively in the oppositedirection so that the full-line pattern 3! which was due predominantlyto the 65-cycle modulation is now reversed in space, assuming that therelative phase difference between the resultant currents at the tworadiators is the same as it was, say about 45. This reversed pattern isshown in dotted line at am in Fig. 3 and is primarily due to the86.7-cycle modulation. The patterns 3! and 3| a are shown overlapping insix places so as to provide six equi-signal courses 33, 34, 35, 36, 31,and 38. Along these courses the 86.7-cycle and 65-cycle modulated wavesmay be heard with equal average intensity.

As the 86.7-cycle modulated wave increases in magnitude and the 65-cyclemodulated wave goes to a minimum, the maximum phase-shift between theresultant waves radiated by the two radiators and 2! will occur again.At this time the 86.7-cycle modulated wave has maximum amplitude and the65-cyc1e modulated wave has minimum amplitude. At this time theradiation will be totally due to the power amplifier M which ismodulated with an 86.7-cycle tone, and the directivity pattern will bethe same as the pattern except that it will be reversed in space asshown. in dotted lines at 30a. The overlap of the patterns 33 and 33acorresponds ractically to the overlap of the patterns 3! and am so thatthe courses defined thereby will correspond practically to the courses33, 34, 35, 3G, 31, and 38.

Thus the phase between the resultant currents at the radiators will beshifted first in one direction and then in the other to provide firstone set of lobular horizontal directivity patterns and a second set oflobular horizontal directivity pat terns similar to the first set ofpatterns but reversed in space and overlapping the first patterns. Thisshifting in the patterns is accomplished through the use of purelyelectrical means without the use of any mechanical or electromechanicalswitching apparatus.

Directivity patterns such as those shown in Figs. 2 and 3 will beradiated more often and persist longer than the pattern shown in Fig. 4.Thus the equi-signal zones defining the beacon courses will be readilrecognizable even though s gnals are radiated according to the patternillustrated in Fig. 4 for relatively short periods during each cycle ofoperation when the two modulated waves have equal amplitudes.

In the example above described, in the areas between courses 33 and 3d,and 36, and 31 and. 38. an 86.7-cycle signal will be received withgreater average intensity than a 65-cycle signal. In the remainingareas, that is, the areas between courses 34 and 35, 35 and 31', and 38and 33, the 65-cycle signal will be received with greater averageintensity than the 86.7-cycle signal. This provides a useful form ofquadrant course identification. For example, an airplane flying awayfrom the line R-R in the general direction of course 33 when providedwith proper receiving equipment can easily identify courses 33 and 38,

since a deviation to the right on course 38 will result in increase inthe relative intensity of the 65-cycle signal while a deviation to theright on course 33 will result in an increase in the relative intensi yof the 86. -cycle signal.

It is not necessary that the modulated waves supplied to the respectiveradiators be modulated by different selected audio frequency modulationsignals, since the waves may also be made separately identifiable eVenthough they are modulated by the same selected audio frequencymodulation signal. For example, the modulators II and I2 may each supplythe same lOOO-cycle modulation signal, for example, to the wavessupplied to the power amplifiers I3 and M. In order to separatelyidentify the modulated signals, the signal supplied by the modulator II, for example, may be interrupted with one code sequence and the othermay be interrupted with a second code sequence which is time-interlockedwith the first code sequence. For example, the modlulations supplied byH may be interrupted in an A manner (dot-dash) and the modulationssupplied by 12 in an interlocking N manner (dash-dot), as is well knownto the art, so that in the equi-signal zones defining the beacon coursesa steady tone is received. An example of an apparatus for coding themodulation is illustrated diagrammatically in Fig. 5. On one side of acourse the A signal is received with greater intensity than the Nsignal, and on the other side of a course the N signal is received withgreater intensity than the A signal. Under such conditions one of themodulators will be operating when the other is not supplying a signaland vice versa. Thus, when the modulator l is operating for example, thdirectivity pattern 30 will be obtained, while when the modulator I2 ioperating the directivity pattern 30a will be obtained and the radiationwill shift rapidly from the pattern 30 to the pattern 30a withoutpassing through the remaining intermediate patterns shown in Figs. 3 and4.

Obviously, other radiator spacings besides three-fourths wavelength canbe used. Also other phase shifts besides 90 can be used. The particularspacing and phase shift depend upon the number and direction of coursesrequired, as well as on the vertical directivity patterns obtained. Thehorizontal directivity patterns for numerous spacings and phaserelations are il lustrated in the Radio Engineering Handbook, secondedition, McGraw-Hill Book Co., 1935, so that the spacings and phaserelations for a given set of conditions may be readily determined. Whenusing the arrangement shown in Fig. 1 it is desirable to modulate boththe 65 and 86.7 waves 100% in order to get the maximum phase differencebetween the currents radiated.

In Fig. 5 I have illustrated a form of my invention adapted to provideaural and visual beacon course indications as well as voice ortelegraphic communication. A carrier frequency source 40 oscillating atany desired frequency, say three megacycles, is shown connected tobalanced modulators a! and 42. A -cycle modulation source 43 is shownconnected to the balanced modulator 4i, and an 86.7-cycle modulationsource 44 is shown connected to the balanced modulator 42. Thus, themodulator 4| delivers carrier-suppressed 65-cycle modulated waves toamplifier 45, and balanced modulator 12 delivers carriersuppressed86.7-cycle modulated waves to amplifier 46. The amplified waves from theamplifiers A5 and 46 are fed through lines 45a and 46a to opposite sidesof a phase-shifting network 41 adapted to produce any desired phaseshift, for example in currents traversing the network. Spaced radiators49 and 50, such as vertical radiator having a length on the order ofone-quarter the carrier frequency wavelength and spaced from one anotherby distances on the order of one-half the carrier frequency wavelength,are shown connected through suitable coupling networks 5| and 52 totransmission lines 53 and 54 which are connected to opposite sides ofthe phase-shifting network 41 and also to amplifiers 45 and 46respectively. Another phase shifting network 41a, giving a phase shiftof 90 for example, is shown connected in the transmission line 53between the coupling device and the lines a.

In the arrangement illustrated in Fig. 5, only the side bands of the 65-and 86.7-cycle waves are radiated from the radiators 49 and 59, sincethe carrier in each of the waves has been suppressed at the balancedmodulator 4| and 42. In order to resupply the carrier frequency to theside bands radiated from 49 and 50, I may provide a non-directionalradiator 55, such as another vertical radiator comparable to theradiators 49 and 50 located centrally, for example, with respect to theradiators 49 and 50. The radiator is shown connected through aphaseshifter 56 and amplifiers 51 and 58 to the source of carrierfrequency 40. The phase-shifter 56 is provided to correct the phase ofthe carrier supplied to the radiator 55 so that the radiated carrierwill have the proper time-phase relationship with respect to the sidebands radiated from 49 and 50, which relation is well known to th art.The use of a suppressed carrier not only permits increased efiiciencyand a saving in power, but also provides a communication channel, sincethe resupplied carrier radiated by the radiator 55 may be modulated byvoice or with other forms of intelligence. The modulated amplifier 58 isprovided for this purpose.

In order to simplify the description we may assume that the resultingcarrier components due to the side bands delivered by the amplifiers 45and 46 are made to arrive at the opposite sides of the phase-shiftingnetwork 4! either in phase or in phase opposition. Since the two wavesresult from modulation by difi'erent modulation frequencies and becausethe carrier has been suppressed, the relation between the carriercomponents of the two waves is periodically shifted The phase betweenthe waves arriving at the network 4'! may be adjusted by inserting suitable phase-shifting networks, if required, in either one or both of thelines 45a and 46a after the manner of the networks |3a and I la shown inFig. 1.

In order to illustrate the relations which bring about the overlappingidentifiable space patterns that produce the radio beacon courses, it isonly necessary to consider the patterns radiated when one of thesupplied waves has zero amplitude and the other wave has a finiteamplitude. When the wave due to the 86.7-cycle modulation has zeroamplitude and the wave due to the -cycle modulation has finiteamplitude, the 65-cycle modulated wave is radiated in phase from theradiators 49 and 50, since it travels through the network 41 in going tothe radiator 50 and duce the horizontal directivity pattern shown indotted lines at 6| in Fig. 6. The wave traveling to the radiator 50 goesdirectly thereto while the wave traveling to the radiator 46 undergoestwo phase shifts due to phase shifters 41 and 41a thereby causing theradiators 49 and 50 to radi- When the 65-cycle ate 180 out of phase orin phase opposition. The patterns 60 and BI are shown intersecting atfour points to produce courses 62, 63, 64, and 65 along which the 65-and 86.7-cycle tones can be heard with equal average intensities.

In Fig. 6 the radiators 49 and 50 are located on a horizontallyextending line R-R and sym metrically disposed with respect to thecenters of the circle surrounding the directivity patterns illustratedin said figure. The patterns are plotted in polar coordinates torepresent the relative amplitudes of the radiated signals as transmittedin any horizontal direction from the centers of the circles at distanceswhich are great compared to the distance between the radiators 49 and50.

The 65- and 86.7-cycle signals are best adapted for visual courseindications, as will be described more completely hereinafter, and I mayalso provide aural course indications as by modulating the carrier inboth of the modulators with a suitable modulation signal, for example1000 cycles, as applied by modulation source 6'! which is connected toboth the balanced modulators 4| and 42 through a coding switch 68operated by a conventional code wheel illustrated diagrammatically at69.

The code wheel may be rotating in the direction of the arrow A and isshown provided with raised portions 10 separated by indented portions H.The switch 68 is provided with a follower 12 adapted to follow thecontour of the code wheel 69 so that the switch 68 makes contact with afixed contact 13 when the follower 12 is riding on the raised surfaces10 of the code wheel. At this time the 1000-cycle modulation is suppliedonly to the balanced modulator 42. When the follower 72 is in contactwith the indented portions 'H of the code wheel, the arm 68 establishesconnection with another fixed contact 14 so that the 1000-cyclemodulation is supplied only to the balanced modulator 4|. By inspectionof Fig. 5, it may be seen that as the wheel 69 rotates, the code letterA will be impressed upon the wave supplied by the amplifier 45 and thecode letter N will be impressed upon the wave supplied by the amplifier46. It will also be seen that the two letters are interlocked so thatthey will be received as a substantially continuous 1000-cycle tone onthe courses 62, 63, 64, and 65, and as either an A or an N in the areasbetween the courses.

When using the suppressed carrier arrangement illustrated in Fig. 5 itis not necessary to modulate the carrier in order to realize the maximumphase shift of the phase-shifting network connected between theradiators as it is with the arrangement in Fig. 1. For example, I mayprovide only 30% modulation with each of the 65 and 86.7 modulationwaves and add thereto a 30% modulation from the 1000-cycle coded wave.The resupplied carrier may also be modulated by the voice modulator 58by another 30%, for example. Although the arithmetic sum of all themodulations supplied to either one of the waves may be more than 100%,the actual modulation is still less than 100%, due to the relation ofthe waves when they are recombined in space.

Obviously, spacings and phase-shifts other than those described inconnection with Fig. 5 may be employed to give the desired number ofcourses, as will be apparent to one skilled in the art, by employing theprinciples detailed herein. It must be remembered, however, thatalthough the horizontal directivity patterns produced by manycombinations of radiator spacing and phase shift appear satisfactory,the vertical directivity of the arrangement must also be considered. Thearrangements illustrated are satisfactory from both horizontal andvertical directivity considerations.

An example apparatus which may be carried by a mobile body such as anairplane for following the beacons provided by the apparatus shown inFigs. 1 and 5 is illustrated diagrammatically in Fig. 7. A conventionalradio receiver 8| is shown with its output connected to magnet coils 8 1and 85 located adjacent to tuned magnetic reeds 80 and Bl which areadapted to vibrate at 65 and 86.7 cycles when the coils of the magnets84 and 85 are energized by currents of those frequencies. Thus a visualindication of the relative magnitudes of the received 65 and 86.7 cyclesmay be obtained by observing the amplitude of vibration of the reeds 8'6and 87. An oncourse heading may be indicated when the reeds 86 and 87vibrate with equal amplitude, and when one reed vibrates with greateramplitude than the other the airplane is known to be located in either a65- or 86.7-cycle zone. Aural indications of position, when using theapparatus illustrated in Fig. 5, may be obtained by connecting theoutput of the receiver 8| to a tuned filter 68 tuned to 1000 cycles forexample and provided with a suitable indicating instrument such as apair of headphones 89. An offcourse position is represented by either anA- tone or an N-tone, while an on-course position is indicated by acontinuous 1000-cycle note.

When using the modulated amplifier 58 to send intelligence such as voiceover the system illustrated in Fig. 5, I may provide the radio receiverwith a filter 90 which is adapted to pass frequencies from about 200 toabout 2000 cycles per second while rejecting the 1000 cycle frequency sothat voice or other intelligence may be heard through earphones 9|without interference from the other fixed tones used in the beaconsystem. Obviously, the receiving apparatus, as well as the transmittingapparatus, is subject to wide modification. For example, I may modulatethe amplifiers H and 12 in Fig, l with 750 and 1000 cycles instead ofthe 65 and 86.7 cycles as illustrated, in which case the reeds 86 and 81would be tuned to 750 and 1000 cycles and the filter 88 would be adaptedto pass the 750- and 1000-cycle signals so that aural as well as visualindications could be obtained. Under such circumstances the filter 90and receiver 9! could be eliminated.

The patterns shown in Figs. 2, 3, 4, and 6 are those obtained when thecurrents at the two radiators are equal. When the ratio of the currentsat two radiators is other than unity the patterns will be shifted withrespect to the line Rr-R about the centers. of the circles enclosing thepatterns. Under such circumstances the resulting courses will makedifferent angles with one another than shown in said figures. Obviously,the resulting courses can be oriented by changing the ratio of thecurrents supplied to the radiators by means well known to the art.

Throughout the specification and in the appended claims the term waveresulting from modulation of a carrier is intended to includesubstantially continuous as well as interrupted Waves. Substantiallycontinuous waves include envelopes resulting from modulation in whichthe amplitudes of the envelopes pass momentarily through zero, andintermittent waves include such envelopes which remain at zero for afinite length of time.

My invention as described in relation to the above illustrative examplesis subject to wide modification, and hence I do not choose to be limitedto the examples described herein, but rather to the scope of theappended claims,

I claim:

1. In the production of a radio beacon through the agency of a pair ofspaced radiators connected to the opposite sides of a phase-shiftingnetwork, the steps of producing a first wave from amplitude modulationof a carrier of given frequency with a first continuous audio frequencysignal and with an intermittent coded signal of a second audio frequencywhile suppressing the carrier; producing a second wave from amplitudemodulation of a carrier of said given frequency with a third continuousaudio frequency signal and with an intermittent coded signal of saidsecond frequency while suppressing the carrier; said coded signals beingapplied in interlocking sequence; continuously supplying said first waveto one of said sides of said network; continuously supplying said secondwave to the other of said sides of said network; and radiating theresultant waves from said radiators,

2. A method as set forth in claim 1, which includes the steps ofmodulating a carrier of said given frequency with a communicationsignal; and radiating said last-named modulated carrier from anon-directional third radiator in proper phase to resupply the carrierto said resultant radiated envelopes.

3. In a radio beacon, the combination which comprises: a pair ofbalanced modulators; a source of carrier waves connected to saidmodulators; means for supplying different modulation frequencies to therespective modulators; a first phase-shifting network having one sideconnected to receive the output from one of said modulators and itsother side connected to receive the output from the other of saidmodulators; a radiator connected to one of said sides of said network; asecond radiator; and a second phase-shifting network connected betweensaid second radiator and the other of said sides of said network.

4. An apparatus as set forth in claim 3, in which said networks eachproduce a phase shift of about at the carrier wave frequency and saidradiators are spaced about one-half a carrier wavelength.

5. An apparatus as set forth in claim 3, which further comprises meansfor supplying a modulation signal of a third audio frequency alternatelyto both of said modulators in an interlocking coded sequence.

6. An apparatus as set forth in claim 3, which further comprises meansincluding a non-directional third radiator for radiating said carrierwave in proper phase relationship to combine with the waves radiatedfrom said first-named radiators.

'7. In the production of a radio beacon through the agency of a pair ofspaced radiators connected to the opposite sides of a phase-shiftingnet-work, the steps of amplitude modulating a carrier with two differentaudio frequency signals to thereby produce two separate waves eachresulting from a different one of such modulations, said waves resultingfrom suppressed carrier modulation; continuously supplying one of saidwaves to one of said sides of said network and continuously supplyingthe other of said waves to the other of said sides of said network;radiating the resultant waves from said radiators; and resupplying thecarrier to said radiated resultant waves in space in proper phaserelationship by radiation from a non-directional third radiator.

8. In a radio beacon, the combination which comprisesi a phase-shiftingnetwork having first and second sides; a source of carrier wavesconnected to said first and second sides of said network; meanscontinuously connected between said source and said first side of saidnetwork for modulating said carrier with an audio frequency signal;means continuously connected between said source and said second side ofsaid network for modulating said carrier with a different audiofrequency signal; and a pair of spaced radiators connected respectivelyto the first and second sides of said network; said network producing aphase shift of about 90 at the carrier frequency and said radiatorsbeing spaced about threequarters of a carrier Wavelength from oneanother.

PAUL J. HOLMES.

